Vapochromic Coordination Polymers for Use in Analyte Detection

ABSTRACT

This application relates to vaprochromic coordination polymers useful for analyte detection. The vapochromism may be observed by visible color changes, changes in luminescence, and/or spectroscopic changes in the infrared (IR) signature. One or more of the above chromatic changes may be relied upon to identify a specific analyte, such as a volatile organic compound or a gas. The chromatic changes may be reversible to allow for successive analysis of different analytes using the same polymer. The polymer has the general formula MW[M′X(Z)Y]N wherein M and M′ are the same or different metals capable of forming a coordinate complex with the Z moiety; Z is selected from the group consisting of halides, pseudohalides, thiolates, alkoxides and amides; W is between 1-6; X and Y are between 1-9; and N is between 1-5. Optionally, an organic ligand may be bound to M. In alternative embodiments of the invention M may be a transition metal, such as Cu and Zn, M′ may be a metal such as Au, Ag, Hg and Cu, and Z may be a pseuodohalide, such as CN, SCN, SeCN, TeCN, OCN, CNO and NNN. In one particular embodiment a new class of [Metal(CN)2]-based coordination polymers with vapochromic properties is described, such as Cu[Au(CN)2]2 and Zn[Au(CN)2]2 polymers.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication Ser. No. 60/618,573 filed 15 Oct. 2004 which is herebyincorporated by reference.

FIELD OF THE INVENTION

This application relates to coordination polymers having vapochromicproperties useful for analyte detection.

BACKGROUND OF THE INVENTION

The controlled design and synthesis of metal-organic coordinationpolymers from the self-assembly of simple molecular building blocks isof intense interest due to the promise of generating functionalmaterials.^(1,2) Vapochromic materials, which display optical absorptionor luminescence changes upon exposure to vapors of analytes, such asvolatile organic compounds (VOCs), have been a focus of attention due totheir potential applications as chemical sensors.⁹⁻¹⁵ For example, whenexposed to certain organic solvents, the extended Prussian BlueCo²⁺—[Re₆Q₈(CN)₆]⁴⁻ (Q=S, Se) system yields dramatic changes in thevisible spectrum that are attributable to the sensed solvent impactingthe geometry and hydration around the Co^(II) centers.¹⁵

Several vapochromic compounds based on Au^(I), Pd^(II), and Pt^(II)coordination polymers have also been reported.⁹⁻¹⁴ The vapochromism inthese systems is based on changes in both the visible absorption andemission spectra. In the linear {Tl[Au(C₆Cl₅)₂]}_(n) polymer, weakinteractions between the Tl atoms and the adsorbed VOC molecules modifyslightly the color, and more significantly the emission spectra.¹² Onthe other hand, changes in the emission spectra of [Pt(CN—R)₄][M(CN)₄](R=iso-C₃H₇ or C₆H₄—C₆H₄—C_(n)H_(2n+1); n=6, 10, 12, 14 and M=Pt, Pd)occur when metal-metal distances are modified due to the presence of VOCmolecules in lattice voids; small changes in the absorption spectrum canalso be observed.^(13,16) Another example is the trinuclear Au^(I)complex with carbeniate bridging ligands, for which its luminescence isquenched in the solid-state when C₆F₆ vapor is adsorbed due to thedisruption of Au—Au interactions.¹¹

Some of these vapochromic materials have recently been incorporated inchemical sensor devices. For example,[Au—(PPh₂C(CSSAuC₆F₅)PPh₂Me)₂][ClO₄] has been used in the development ofan optical fiber volatile organic compound sensor.¹⁷ A vapochromic lightemitting diode¹⁸ and a vapochromic photodiode¹⁹ have also been builtusing tetrakis(p-dodecylphenylisocyano) platinum tetranitroplatinate andbis(cyanide)-bis(p-dodecylphenylisocyanide)platinum(II), respectively.

In these previous discoveries, slight shifts in the ν_(CN) stretch areobserved if hydrogen-bonding between the N(cyano) atoms and the VOCmolecules present in the lattice occurs. Importantly, VOCs cannot bereadily differentiated or identified via IR spectroscopy in this casesince ν_(CN) shifts of only 0-10 cm⁻¹ are usually observed.^(17,54,55)

To overcome the shortcomings of the prior art, the need has arisen forcoordination polymers having improved vapochromic properties forenhancing the sensitivity of analyte detection. The IR signaturesachieved by the present invention are unusually diagnostic for aparticular analyte, both in the number and position of the IR bands. Inthe case of some gases, the adsorption of the analyte to the polymersubstantially enhances the IR response. That is, the response in theν_(CN) or other pertinent region of the spectrum is extremely strongcompared to the direct IR-signature of some gases, which is the currentstate-of-the-art in gas sensors. Moreover, in the present invention thevapochromism of polymers can be readily and reversibly observed bymultiple means, such as visible colour changes and luminescence changesin addition to IR spectroscopic changes.

SUMMARY OF THE INVENTION

In accordance with the invention, a vapochromic polymer is describedhaving the general formula M_(W)[M′_(X)(Z)_(Y)]_(N) wherein M and M′ arethe same or different metals capable of forming a coordinate complexwith the Z moiety; Z is selected from the group consisting of halides,pseudohalides, thiolates, alkoxides and amides; W is between 1-6; X andY are between 1-9; and N is between 1-5. For example, in one embodimentW and X are 1 and Y and N are 2.

The vapochromic properties of the polymer change when the polymer isexposed to different analytes. The polymer may therefore be used foranalyte detection. The vapochromism may be observed by visible colorchanges, changes in luminescence, and/or spectroscopic changes in theinfrared IR signature. One or more of the above chromatic changes may berelied upon to identify a specific analyte, such as a volatile organiccompound or a gas. The chromatic changes may be reversible to allow forsuccessive analysis of different analytes using the same polymer.

In alternative embodiments of the invention M may be a transition metal,such as Cu and Zn, M′ may be a metal such as Au, Ag, Hg and Cu, and Zmay be a pseuodohalide, such as CN, SCN, SeCN, TeCN, OCN, CNO and NNN.Optionally, an organic ligand may be bound to M. In one particularembodiment a new class of [Metal(CN)₂]-based coordination polymers withvapochromic properties is described, such as Cu[Au(CN)₂]₂ andZn[Au(CN)₂]₂ polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which describe embodiments of the invention but which shouldnot be construed as restricting the spirit or scope of the invention inany way,

FIG. 1 is a diagram of the 1-D crystal structure of a first polymorph ofCu[Au(CN)₂]₂(DMSO)₂. DMSO-methyl groups were removed for clarity.

FIGS. 2(a) and (b) are diagrams of the 3-D crystal structure of thefirst polymorph of Cu[Au(CN)₂]₂(DMSO)₂.

FIGS. 3(a) and (b) are diagrams of the 2-D and 3-D crystal structure ofa second polymorph of Cu[Au(CN)₂]₂(DMSO)₂.

FIG. 4 is a graph showing the thermal stability of the first and secondpolymorphs of Cu[Au(CN)₂]₂(DMSO)₂.

FIG. 5 is a photograph showing the vapochromic behavior of the secondpolymorph of Cu[Au(CN)₂]₂(DMSO)₂ after exposure to various analytes,namely DMSO, water, MeCN, DMF, Dioxane, Pyridine and NH₃.

FIGS. 6(a) and (b) are diagrams of the 2-D and 3-D crystal structure ofCu[Au(CN)₂]₂(DMF).

FIGS. 7(a) and (b) are diagrams of the 2D crystal structure ofCu[Au(CN)₂]₂(pyridine)₂.

FIG. 8 is a diagram of the postulated 2-D crystal structure of a solventfree complex of Cu[Au(CN)₂]₂.

FIG. 9 are photographs showing changes in luminescence in theZn[Au(CN)₂]₂(analyte)_(x) system (top—under room light; bottom—under UVlight). From left to right: Analyte=None, NH₃, pyridine, CO₂, DMSO.

FIG. 10 is a spectrograph showing the comparative IR spectra in thecyanide region for three analytes (solvents), namely pyridine, DMF andwater using the Cu[Au(CN)₂]₂(solvent), polymer.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following description specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the present invention.Accordingly, the specification and drawings are to be regarded in anillustrative, rather than a restrictive, sense.

This application relates to vapochromic polymers useful for detection ofanalytes. The polymers have the general formula M_(W)[M′_(X)(Z)_(Y)]_(N)wherein M and M′ are the same or different metals capable of forming acoordinate complex in conjunction with the Z moiety; Z is selected fromthe group consisting of halides, pseudohalides, thiolates, alkoxides andamides; W is between 1-6; X and Y are between 1-9; and N is between 1-5.As will be apparent to a person skilled in the art and as describedherein, the vapochromic polymers of the invention may also compriseother constituents including ligands, counterbalancing ions and othermetals. The invention encompasses polymers having the same empiricalformula as set out above which exhibit vapochromic properties.

As described below, the vapochromism of the polymers may be observed,for example, by (1) visible changes, such as changes in colour orluminescence upon exposure to analytes, and by (2) infrared (IR)spectroscopic changes. The invention thus provides multiple detectionmeans or “channels” to thereby achieve highly sensitive analytedetection. As used in this patent application the term “vapochromic”refers to a material that has a spectroscopic property change uponexposure to a gas or liquid analyte (e.g. a volatile organic compound)and the term vapochromism refers to such a spectroscopic propertychange. The spectroscopic property may include any wavelength of lightincluding microwaves, infrared, visible colour and luminescence. As usedin this patent application the process of “detecting chromatic changes”includes detecting a spectroscopic property change, including bothvisible and non-visible changes resulting from exposure to an analyte.

As exemplified by the Examples described below, in some embodiments ofthe invention M is a transition metal such as copper (Cu) or zinc (Zn)and M′ is a metal such as gold (Au), silver (Ag), mercury (Hg) orcopper. The Z moiety may be an ion or anionic ligand. Suitable Zmoieties include pseudohalide ions such as CN—. As will be apparent to aperson skilled in the art, other suitable pseudohaldides include SCN,SeCN, TeCN, OCN, CNO and NNN. In particular embodiments of the inventionCu[Au(CN)₂]₂ and Zn[Au(CN)₂]₂ polymers are described. The Cu[Au(CN)₂]₂embodiment takes advantage of the unique chemical properties of gold (I)and copper (II) ions, such as attractive gold-gold interactions andluminescence for gold and a flexible coordination sphere for copper. Theattractive interactions enable the formation of chemically stable,high-dimensionality materials and the gold-luminescence, cyanide-IR andcopper(II) visible spectrum can all act as simultaneous sensory outputs.Similarly, with respect to the Zn[Au(CN)₂]₂ embodiment, distinctiveluminescence and other photochromic qualities are exhibited.

In other embodiments of the invention the metal M may be a 1^(st) rowtransition metal other than Cu or Zn, such as Sc, Ti, V, Cr, Mn, Fe, Co,or Ni, or some other transition-metal such as Zr, Nb or Ru. M may alsobe a lanthanide. Although the Mn (water)⁴⁰, Fe (with K-salt)⁴⁰, Co(none, with K-salt^(56,57), and DMF⁴¹), Zn (none)⁵⁸ and a fewlanthanides (Gd, Eu, Yb—all with no ligands)^(52,59-61) complexes areknown in the prior art (ligands shown in brackets), no sensor orvapochromic properties for such complexes have been previouslydescribed.

Optionally, an organic ligand may be bound to M. The ligand may be anyligand capable of capping the metal cation, and may include nitrogen,oxygen, sulfur or phosphorus donors.

Depending upon the resultant charge of the M_(W)[M′_(X)(Z)_(Y)]_(N)structure, a charge-balancing ion, either a cation or anion, may also bepresent. For example, a charge balancing ion may be required where M′ isHg.

In alternative embodiments of the invention the metal M′ may be selectedto produce both linear metal cyanides or non-linear cyanides. Forexample, cyanometallate units such as [Au(CN)₂]⁻, [Ag(CN)₂]⁻ or[Hg(CN)₂] may be incorporated into polymers in conjunction withdifferent transition metal cations and supporting ligands according tothe following general equation:^(31-33,63-68)[METAL cation+organicligand_(z)]^(n+)+[M′(CN)_(x)]^(y)→METAL(ligand)_(z)][M′(CN)_(x)]_(n)(n=1-5, x=2-9, y=−5 to 0, z=0-9)

The synthesis may be readily accomplished in solvents such as water oralcohols. Compared to prior art approaches, the polymers andpolymer-analyte compositions of the present invention can be preparedfrom extremely simple commercially available starting materials inminimal steps. As described in the Examples section below, the syntheticmethodology, which has built-in design flexibility, low-cost and simplesynthesis, is also a general advantage of coordination polymer systemsover current zeolitic technology. The system is modular in that themetal cation and organic ligand can be chosen as desired to target aparticular application or property.

An important advantage of embodiments of the invention described hereinis that the vapochromic properties of the polymers may be reversible.For example, the Cu[Au(CN)₂]₂ embodiment shows reversible vapochromicsensor behaviour attributable to the Cu—Au pairing.⁶² Starting with asolid of any Cu[Au(CN)₂]₂(solvent)_(x), addition of a different solventvapour (analytes) generates a new complex. As described below,exceptions may apply in the case of very strong donor solvents such aspyridine or ammonia, which bind strongly to the Cu^(II) center and arenot easily displaced by other solvents. Similarly, the Zn[Au(CN)₂]₂embodiment exhibits reversible vapoluminescent material qualities.⁶⁹ Thepolymers of the invention may thus be employed in a dynamic system forsuccessively detecting different analytes without the need forreinitialization (although reinitialization may still be required torepeatedly detect the same analyte).

The invention may be used for detecting a wide variety of analytesincluding volatile organic compounds (VOCs) and gases. The solidpolymers adsorb (i.e. bind or trap) analyte, such as organic solvents,exposed to the polymers in a vapour (or liquid) phase. The detectableVOCs typically include a hetero (non-carbon) atom donor such ashydrogen, nitrogen, oxygen, sulfur and phosphorus donors. Examples ofsolvent vapours that will effectively adsorb to the polymers of theinvention include pyridine, dioxane, water, ethanethiol andtrimethylphosphine. Donor gases such as H₂S and ammonia also readilybind and are detectable. The binding capacity and sensitivity of thepolymers may be adjusted through altering the identity of the metals Mand M′ to enable detection of a range of gases, including but notlimited to NO_(x), SO_(x), CO_(x) and allenes. For example, thezinc-based polymer described herein appears to bind CO and CO₂ and mayhave applications as a CO or CO₂-sensor.

As will be appreciated by a person skilled in the art, the polymers ofthe invention may find application in wide range of industrial andcommercial applications, such as in the chemical, energy andenvironmental sectors. The polymers may be used in many different solidforms depending upon the vapochromic application, such as powders,crystals, thin films or combinations thereof. Exemplary industrialapplications include: personal and badge monitors in chemicallaboratories (e.g. industrial chemical or pharmaceutical researchlaboratories, paint and coatings manufacturing, cosmetics manufacturing)for hazardous vapour detection; portable or stationary thresholdmonitors for chemical vapours in laboratory environments or chemicalstorage facilities for hazardous vapour detection or regulated emissionrequirements; environmental sensor for volatile organic compounds orgases (“electronic noses”) for use at environmental remediation sites,landfills, air-quality monitoring etc.; and responsive coatings, artsupplies, colour-changing paint and other related applications where acolour-changing material is desired.

Although the present invention has been principally described inrelation to analyte sensing and detection, the polymers and compositionsdescribed herein may be useful for other purposes such as extraction,purification and storage applications.

EXAMPLES

The following examples will further illustrate the invention in greaterdetail although it will be appreciated that the invention is not limitedto the specific examples.

The following description of experimental details and experimentalresults is presented in multiple parts. Example 1.0 describes syntheticprocedures and experimental results for the Cu[Au(CN)₂]₂(solvent)_(x)system. Example 2.0 briefly describes a similar synthetic procedure andexperimental results for an analogous Zn[Au(CN)₂]₂(solvent)_(x) system.

Example 1.0 1.1 Cu[Au(CN)₂]₂(solvent)_(x) System

1.1.1 Experimental Apparatus and General Procedure

General Procedure and Physical Measurements. All manipulations wereperformed in air. All the reagents were obtained from commercial sourcesand used as received. Infrared spectra were recorded as KBr pressedpellets on a Thermo Nicolet Nexus 670 FT-IR spectrometer. Microanalyses(C, H, N) were performed at Simon Fraser University. Magneticsusceptibilities were measured on polycrystalline samples at 1 T between2 and 300 K using a Quantum Design MPMS-5S SQUID magnetometer. All datawere corrected for temperature independent paramagnetism (TIP), thediamagnetism of the sample holder, and the constituent atoms (by use ofPascal constants).²⁰ Solid-state UV-visible reflectance spectra weremeasured using an Ocean Optics SD2000 spectrophotometer equipped with atungsten halogen lamp. Thermogravimetric analysis (TGA) data werecollected using a Shimadzu TGA-50 instrument in an air atmosphere.

Synthesis of Cu[Au(CN)₂]₂(DMSO)₂, 1: A 0.5 mL dimethylsulfoxide (DMSO)solution of Cu(ClO₄)₂.6H₂O (0.037 g, 0.1 mmol) was added to a 0.5 mLDMSO solution of KAu(CN)₂ (0.057 g, 0.2 mmol). Green crystals ofCu[Au(CN)₂]₂(DMSO)₂ were obtained by slow evaporation over several days,filtered and air-dried. Yield: 0.050 g, 70%. Anal. Calcd. forC₈H₁₂N₄Au₂CuO₂S₂: C, 13.39; H, 1.69; N, 7.81. Found: C, 13.43; H, 1.72;N, 7.61. IR (KBr): 3005(w), 2915(w), 2184(s), 2151(m), 1630(w), 1426(w),1408(w), 1321(w), 1031(m), 993(s), 967(m), 720(w), 473(m) cm⁻¹. The sameproduct can be obtained by absorption of DMSO by Cu[Au(CN)₂]₂(H₂O)₂.

Synthesis of Cu[Au(CN)₂]₂(DMSO)₂, 2: A 0.2 mL DMSO solution ofCu(ClO₄)₂.6H₂O (0.037 g, 0.1 mmol) was added to a 0.4 mL DMSO solutionof KAu(CN)₂ (0.057 g, 0.2 mmol). Blue needles of Cu[Au(CN)₂]₂(DMSO)₂formed after one hour and were filtered and dried under N₂. Yield: 0.057g, 80%. Anal. Calcd. for C₈H₁₂N₄Au₂CuO₂S₂: C, 13.39; H, 1.69; N, 7.81.Found: C, 13.50; H, 1.76; N, 7.62. IR (KBr): 3010(w), 2918(w), 2206(m),2194(s), 2176(m), 2162(m), 1631(w), 1407(w), 1316(w), 1299(w), 1022(m),991(s), 953(m), 716(w), 458(m) cm⁻¹.

Synthesis of Cu[Au(CN)₂]₂(DMF), 3: A 2 mL N,N-dimethylformamide (DMF)solution of Cu(ClO₄)₂.6H₂O (0.037 g, 0.1 mmol) was prepared. Thissolution was added to a 3 mL DMF solution of KAu(CN)₂ (0.057 g, 0.2mmol). A dark blue-green mixture of powder and crystals ofCu[Au(CN)₂]₂(DMF) was obtained after several days of slow evaporationand was filtered and air-dried. Yield: 0.033 g, 52%. Anal. Calcd forC₇H₇N₅Au₂CuO: C, 13.25; H, 1.11; N, 11.04. Found: C, 13.26; H, 1.11; N,11.30. IR (KBr): 2927(w), 2871(w), 2199(s), 2171(shoulder), 1665(s),1660(s), 1492(w), 1434(w), 1414(w), 1384(m), 1251(w), 1105(w), 674(w),516(w), 408(w) cm⁻¹. Single crystals of 3 were obtained by dissolvingCu[Au(CN)₂]₂(H₂O)₂ (5) in DMF and allowing the solution to evaporatevery slowly. The single crystals and the crystal/powder mixture asprepared above had identical IR spectra. The same product can also beobtained by vapour absorption of DMF by severalCu[Au(CN)₂]₂(solvent)_(x) complexes.

Synthesis of Cu[Au(CN)₂]₂(pyridine)₂, 4: A 10 mL pyridine/water/methanol(5:47.5:47.5) solution of Cu(ClO₄)₂.6H₂O (0.111 g, 0.3 mmol) wasprepared. This solution was added to a 10 mL pyridine/water/methanol(5:47.5:47.5) solution of KAu(CN)₂ (0.171 g, 0.59 mmol). A blue powderof Cu[Au(CN)₂]₂(pyridine)₂ was obtained immediately and was filtered andair-dried. Yield: 0.163 g, 75%. Anal. Calcd for C₁₄H₁₀N₆Au₂Cu: C, 23.36;H, 1.40; N, 11.68. Found: C, 23.52; H, 1.44; N, 11.58. IR (KBr):3116(w), 3080(w), 2179(s), 2167(s), 2152(s), 2144(m), 1607(m), 1449(m),1445(s), 1214(m), 1160(w), 1071(m), 1044(w), 1019(m), 758(s), 690(s),642(m) cm⁻¹. Single crystals of 4 were obtained by slow evaporation ofthe remaining solution. The crystals and powder had identical IRspectra. The same product can also be obtained by vapour absorption ofpyridine by several Cu[Au(CN)₂]₂(solvent)_(x) complexes.

Synthesis of Cu[Au(CN)₂]₂(H₂O)₂, 5: A 10 mL aqueous solution ofCu(ClO₄)₂.6H₂O (0.259 g, 0.7 mmol) was prepared and added to a 10 mLaqueous solution of KAu(CN)₂ (0.403 g, 1.4 mmol). A pale green powder ofCu[Au(CN)₂]₂(H₂O)₂ formed immediately and was filtered and air-dried.Yield: 0.380 g, 91%. The same product can be obtained by vapourabsorption of water by several Cu[Au(CN)₂]₂(solvent), complexes. Anal.Calcd for C₄H₄N₄Au₂CuO₂: C 8.04, H 0.67, N 9.38. Found: C, 8.18; H,0.71; N, 9.22. IR (KBr): 3246(m), 2217(s), 2194(vw), 2171(s), 1633(w)cm⁻¹.

Synthesis of Cu[Au(CN)₂]₂, 6: Cu[Au(CN)₂]₂(H₂O)₂ was heated (150° C.) invacuo to yield green-brown Cu[Au(CN)₂]₂. The yield is quantitative, withno ν_(CN) peaks for hydrated 5 observable. Anal. Calcd for C₄N₄Au₂Cu: C8.56, H O, N 9.98. Found: C 8.68, H trace, N 9.80. IR (KBr): 2191(s),1613(vw), 530(m) cm⁻¹.

Synthesis of Cu[Au(CN)₂]₂(CH₃CN)₂, 7: A 1 mL CH₃CN solution ofCu(ClO₄)₂.6H₂O (0.037 g, 0.1 mmol) was prepared and added to a 2 mLCH₃CN solution of KAu(CN)₂ (0.057 g, 0.2 mmol). A green powder ofCu[Au(CN)₂]₂(CH₃CN)₂ precipitated immediately along with a white powderof KClO₄. To prevent the replacement of CH₃CN by atmospheric water, thesolvent was removed under vacuum and the KClO₄ side product was notremoved through washing and filtering. Anal. Calcd forCu[Au(CN)₂]₂(CH₃CN)₂+2(KClO₄) (C₈H₆N₆Au₂Cl₂CuK₂O₈): C, 10.44; H, 0.65;N, 9.12. Found: C, 10.99; H, 0.57; N, 8.69. IR (KBr): 2297(w), 2269(w),2192(s), 1600(w), 1445(w), 1369(w), 1088(s), 941(w), 925(w), 752(w),695(w), 626(m), 512(w), 468(w), 419(w) cm⁻¹. The same product (withoutKClO₄) can be obtained by vapour absorption of acetonitrile byCu[Au(CN)₂]₂(DMSO)₂ (1 or 2).

Synthesis of Cu[Au(CN)₂]₂(dioxane)(H₂O), 8: A 2 mL dioxane/water (2:1)solution of Cu(ClO₄)₂.6H₂O (0.037 g, 0.1 mmol) was prepared. Thissolution was added to a 4 mL dioxane/water (2:1) solution of KAu(CN)₂(0.057 g, 0.2 mmol). A pale blue-green powder ofCu[Au(CN)₂]₂(dioxane)(H₂O) was obtained immediately and was filtered andair-dried. Yield: 0.057 g, 85%. The same product can be obtained byvapour absorption of dioxane by several Cu[Au(CN)₂]₂(solvent)_(x)complexes (the water molecule included in this case is from ambientmoisture). Anal. Calcd for C₈H₁₀N₄Au₂CuO₃: C, 14.39; H, 1.51; N, 8.39.Found: C, 14.31; H, 1.21; N, 8.43. IR (KBr): 2976(m), 2917(m), 2890(w),2862(m), 2752(w), 2695(w), 2201(s), 2172(w), 1451(m), 1367(m), 1293(w),1255(s), 1115(s), 1081(s), 1043(m), 949(w), 892(m), 871(s), 705(w),610(m), 515(m), 428(m) cm⁻¹.

Synthesis of Cu[Au(CN)₂]₂(NH₃)₄, 9: This product was obtained by vapourabsorption of NH₃ by several Cu[Au(CN)₂]₂(solvent)_(x) complexes. Theyield is quantitative as shown by IR. Anal. Calcd for C₄H₁₂N₈Au₂Cu: C7.63, H 1.92, N 17.80, found: C, 7.56; H, 1.98; N, 17.71. IR (KBr):3359(s), 3328(s), 3271(s), 3212(m), 3182(m), 2175(m), 2148(s), 1639(m),1606(m), 1243(s), 685(s), 435(w) cm⁻¹.

X-Ray Crystallographic Analysis. Cu[Au(CN)₂]₂(DMSO)₂ 1 and 2,Cu[Au(CN)₂]₂(DMF) 3 and Cu[Au(CN)₂]₂(pyridine)₂ 4: Crystallographic datafor all structures are collected in Table 1. Crystals 1, 3 and 4 weremounted on glass fibers using epoxy adhesive and crystal 2 was sealed ina glass capillary. Crystal 1 was a green rectangular plate(0.09×0.12×0.3 mm³), crystal 2 was a pale blue needle (0.11×0.11×0.2mm³), crystal 3 was a green needle (0.09×0.09×0.15 mm³) and crystal 4was a dark blue platelet (0.02×0.06×0.15 mm³).

For 1, data in the range 4°<2θ<55° were recorded using thediffractometer control program DIFRAC²¹ and an Enraf Nonius CAD4Fdiffractometer. The NRCVAX Crystal Structure System was used to performpsi-scan absorption correction (transmission range: 0.0301-0.1726) anddata reduction, including Lorentz and polarization corrections.²² Allnon-hydrogen atoms were refined anisotropically. Full matrixleast-squares refinement (1231 reflections included) on F (93parameters) converged to R₁=0.042, wR₂=0.047 (I_(o)>2.5σ(I_(o))).

For 2, 3 and 4, data in the ranges 6.9°<2θ<136.1°, 9.2°<2θ<144.0° and12.0°<2θ<142.6° respectively were recorded on a Rigaku RAXIS RAPIDimaging plate area detector. A numerical absorption correction wasapplied (transmission range: 0.019-0.161, 0.0070-0.0199 and0.3484-0.5826) and the data were corrected for Lorentz and polarizationeffects.²³ For 2, the Au, Cu and S atoms were refined anisotropically,while the remainders were refined isotropically. For 3 and 4, allnon-hydrogen atoms were refined anisotropically. Full matrixleast-squares refinement on F was performed on 2, 3 and 4, the dataconverging to the following results: for 2, R₁=0.062, wR₂=0.082(I_(o)>3.0σ(I_(o)), 2026 reflections included, 205 parameters); for 3,R₁=0.0315, wR₂=0.0456 (I_(o)>3.0σ(I_(o)), 1538 reflections included, 148parameters); for 4, R₁=0.0276, wR₂=0.0401 (I_(o)>3.0σ(I_(o)), 1021reflections included, 107 parameters).

All structures were refined using CRYSTALS.²⁴ The structures were solvedusing Sir 92 and expanded using Fourier techniques. Hydrogen atoms wereincluded geometrically in all structures but not refined. Diagrams weremade using Ortep-3 (version 1.076)²⁵ and POV-Ray (version 3.6.0)²⁶.Selected bond length and angles for 1-4 are reported in Tables 2 to 5respectively.

1.1.2 Results

Synthesis. The reaction of Cu^(II) salts with KAu(CN)₂ indimethylsulfoxide (DMSO) produced two different compounds, depending onthe total concentration of starting reagents. In dilute solution, greencrystals of polymorph 1 formed slowly, whereas blue crystals ofpolymorph 2 were obtained rapidly in a highly concentrated solution. TheIR spectra of 1 and 2 show different features (Table 6); thehigher-energy bands likely correspond to bridging CN-groups, while thelower-energy bands are due to either free or loosely bound CN-groups.²⁷The X-ray crystal structures of 1 and 2 revealed two different polymericnetworks, both with the same empirical formula Cu[Au(CN)₂]₂(DMSO)₂, asconfirmed by elemental analysis.

Crystal Structure of the Green Cu[Au(CN)₂]₂(DMSO)₂ Polymorph, 1. Thefive-coordinate Cull center in 1 has a τ-value²⁸ of 0.44, where τ=0 ispure square pyramidal and τ=1 is pure trigonal bipyramidal, suggestingthat the coordination geometry could be considered equally distortedfrom either polyhedron. The Cu^(II) center is bound to two DMSO-O atoms(O—Cu—O=167.06°) and three N(cyano) atoms (FIG. 1). Selected bondlengths and angles for 1 are listed in Table 2. The asymmetric unitcontains two different [Au(CN)₂]⁻ units: a CuI-bridging moiety thatgenerates a 1-D chain, and a Cu^(II)-bound dangling group. The chainsstack on top of each other parallel to the (101)-plane, forming stacksof chains that are offset to allow interdigitation of the dangling[Au(CN)₂]⁻ units. Each chain is connected to the four neighbouringchains through Au—Au interactions of 3.22007(5) A between the Au(1)atoms of each dangling group and the Au(2) atoms of the chain backbone(FIG. 2(a)). The DMSO molecules occupy the channels between the chains;these channels are delineated by both [Au(CN)₂] groups and Au—Au bonds(FIG. 2(b)). A viable Au—Au interaction is considered to exist when thedistance between the two atoms is less than 3.6 Å, the sum of the vander Waals radii for gold.²⁹

Crystal Structure of the Blue Cu[Au(CN)₂]₂(DMSO)₂ Polymorph, 2. Thestructure of polymorph 2 contains Cu^(II) centers in a Jahn-Tellerdistorted octahedral geometry, with the two DMSO molecules bound in acis-equatorial fashion (O—Cu—O=95.2°) rather than in the nearly180°-arrangement in 1. Selected bond lengths and angles for 2 are foundin Table 3. The four remaining sites (two axial and two equatorial) areoccupied by N(cyano) atoms of bridging [Au(CN)₂]⁻ units, generatingcorrugated 2-D sheets (FIG. 3(a)). These 2-D layers stack (FIG. 3(b))and are held together by weak Au(1)-Au(2) interactions of 3.419(3) Å andperhaps weak Au(3) . . . Au(4) contacts of 3.592(4) Å. Thus, the colourdifference between the two polymorphs can be attributed to the differentcoordination number and geometry around the Cu^(II) centers. That said,the coarse features of 1, namely the rectangular “channels” filled withDMSO molecules, are also clearly delineated in 2.

Magnetic Properties. As polymorphs 1 and 2 clearly have significantlydifferent solid-state structures, it follows that their physical andchemical properties may also vary; this is obviously the case for theirsolid-state optical reflectance spectra, which show λ_(max) of 550±7 and535±15 nm respectively (Table 6). To explore this key issue, a series ofrepresentative properties were investigated. For example, the magneticsusceptibilities of 1 and 2 were measured at temperatures varying from300 to 2 K. At 300 K, μ_(eff)=1.98 and 1.93μ_(B) for 1 and 2respectively, typical for Cu^(II) centers.³⁰ As the temperature drops,μ_(eff) decreases and reaches 1.74 and 1.67μ_(B) at 2 K for 1 and 2respectively. There is no maximum in either χ_(M) vs T plot. Thisbehaviour is consistent with weak antiferromagnetic coupling, probablymediated by the diamagnetic Au^(I) center.³¹⁻³⁴ Thus, the two polymorphshave similar magnetic properties.

Thermal stability. Examining the thermal stabilities of 1 and 2 bythermogravimetric analysis (FIG. 4), 1 loses its first DMSO moleculefrom 150-190° C. and the other one from 210-250° C. For polymorph 2(which has 4 crystallographically distinct DMSO molecules), the firsttwo DMSO molecules are lost between 100-135° C. and then 150-190° C.,while the two remaining DMSO molecules dissociate around 210-250° C.,comparable with 1. Both polymorphs are then stable until 310° C., atwhich point cyanogen (C₂N₂) is released, consistent with thedecomposition of the Cu[Au(CN)₂]₂ framework.³⁵ Hence, the thermalstabilities of the two polymorphs with respect to the loss of the firstDMSO molecules are significantly different. Differential scanningcalorimetry shows no evidence for the thermal interconversion in thesolid state from 2 to 1 below the decomposition temperature of 2.

Vapochromic Behavior. Interestingly, even though both polymorphs arethermally stable up to at least 100° C., the DMSO molecules can easilybe replaced by ambient water vapour at room temperature to yieldCu[Au(CN)₂]₂(H₂O)₂ (5), as shown by elemental and thermogravimetricanalysis. Despite the fact that both polymorphs have differentsolid-state structures, IR spectroscopy and powder X-ray diffractionshow that both polymorphs convert to the same Cu[Au(CN)₂]₂(H₂O)₂ (5)complex (Table 6). This conversion is reversible. However, if DMSOvapour is added back to 5, only the green polymorph Cu[Au(CN)₂]₂(DMSO)₂(1) is formed, even if the original DMSO-complex to which H₂O was addedwas the blue polymorph (2). The exchange of DMSO for H₂O can be observedvisually from the associated colour change (FIG. 5).

Cu[Au(CN)₂]₂(DMSO)₂ (either 1 or 2) also displays vapochromic behaviourwhen exposed to a variety of other donor solvent vapours (i.e. analytes)in addition to H₂O. Each Cu[Au(CN)₂]₂(solvent)_(x) complex can bedistinguished easily by its colour (FIG. 5 and Table 6). In addition,the ν_(CN) region of the IR spectrum for each solvent complex is acharacteristic, sensitive signature for that solvent (Table 6). FIG. 10is a spectrograph showing the comparative IR spectra in the cyanideregion for three solvents (i.e. analytes), namely pyridine, DMF andwater using the Cu[Au(CN)₂]₂(solvent)_(x) polymer. FIG. 10 showgraphically the characteristic, sensitive signature for each solvent inthe vCN region of the IR spectrum. Thus both the visible colour changesand the cyanide-IR changes are dramatic and distinctive for eachanalyte, allowing for more specific and sensitive analyte detection.

Importantly, this solvent exchange is completely reversible, thuspermitting dynamic solvent sensing. As indicated in the above syntheticexamples, starting with a solid of Cu[Au(CN)₂]₂(solvent)_(x), additionof a different solvent vapour generates a new complex. The onlyexceptions occur in the case of very strong donor solvents such aspyridine or ammonia, which bind strongly to the Cu^(II) center and arenot easily displaced by other solvents.

Each Cu[Au(CN)₂]₂(solvent), complex was also synthesized by reactingCu(II) salts with [Au(CN)₂]⁻ in the appropriate solvent and each wasfound, by elemental analysis, IR spectroscopy, TGA, and crystallography,to be identical to the complex generated by solvent exchange. In everycase, elemental analysis and TGA (Table 7) indicate that the number ofsolvent molecules incorporated into the complex per transition metalcenter is always the same as the number incorporated by vapouradsorption. This is easily rationalized by the fact that all adsorbedsolvent molecules are ligated to the Cu^(II) center in a 1:1, 1:2 or, inthe case of ammonia, a 1:4 ratio, with no additional loosely trappedsolvent molecules in channels (as shown by TGA, Table 7), as is oftenobserved in other porous systems that include solvent.³⁶⁻³⁹

Crystal Structure of Cu[Au(CN)₂]₂(DMF), 3. In order to better understandthe structural changes that occur during a vapochromic response of theDMSO polymorphs, the structures of Cu[Au(CN)₂]₂(DMF) (3) andCu[Au(CN)₂]₂(pyridine)₂ (4) were investigated. The structure of 3contains Cu^(II) centers with a square-pyramidal geometry, where thefour basal sites are occupied by N(cyano) atoms of bridging [Au(CN)₂]⁻units and the apical site is occupied by an O-bound DMF molecule.Selected bond lengths and angles for 3 are listed in Table 4. Thealternation of Cull centers and [Au(CN)₂]⁻ units generates a 2-D squaregrid motif with all the DMF molecules pointing either above or below theplane of the sheet (FIG. 6(a)). This grid is similar to that observed inthe blue Cu[Au(CN)₂]₂(DMSO)₂ complex (2) if one DMSO molecule wasremoved and the corrugation reduced. The layers stack on top of eachother in an offset fashion, thereby disrupting any channels, and areheld together by Au(1)-Au(1*^(a)) and Au(2)-Au(2*^(b)) interactions of3.3050(12) Å and 3.1335(13) Å (FIG. 6(b)).

Crystal Structure of Cu[Au(CN)₂]₂(pyridine)₂, 4. The structure of 4 issimilar to that of 3, except that the Cu^(II) centers are surrounded bytwo solvent molecules, generating octahedrally coordinated metals. Theaxial sites and two of the equatorial sites are occupied by N(cyano)atoms of bridging [Au(CN)₂]⁻ units. Pyridine molecules occupy the twoother equatorial sites. Selected bond lengths and angles for 4 arelisted in Table 5. As observed for 3, infinite 2-D layers are obtained(FIGS. 7(a) and (b)). No aurophilic interactions are present between theAu atoms of neighboring sheets, but π-π interactions of ˜3.4 Å are foundbetween stacked pyridine rings of adjoining sheets. Thus, thesquare-grid array present in 2 and 3 is maintained but in this case thesheets are completely flat, as opposed to the corrugated array found in2. The 180° disposition of the pyridine rings (vs. the cis orientationof the DMSO molecules in 2) also serves to separate the sheets,disrupting potential intersheet Au—Au interactions.

Solvent free Cu[Au(CN)₂]₂, 6. The green-brown solvent-free complex,Cu[Au(CN)₂]₂ (6), was also prepared by thermally removing in vacuo thewater molecules from 5. Changes in the powder X-ray diffractogram and inthe ν_(CN) peaks of 6 indicate that some rearrangement in the frameworkoccurred. The IR spectrum only shows one stretching frequency (2191cm⁻¹), indicating that all CN groups are in a similar environment,reminiscent of the Cu[Au(CN)₂]₂(DMF) structure. This is also comparablewith the results published for the Mn[Au(CN)₂]₂(H₂O)₂ ⁴⁰ and theCo[Au(CN)₂]₂(DMF)₂ ⁴¹ systems (which show stretches at 2150 and 2179cm⁻¹ respectively). In these two coordination polymers, the M[Au(CN)₂]₂unit (M=Mn or Co) forms 2-D square grids, with solvent molecules hangingabove and below the plane of the sheet. Although the three-dimensionaltopology of Cu[Au(CN)₂]₂ is not known, it likely forms a similar 2-Dsquare grid network with all N(cyano) atoms equatorially bound to asquare planar Cu^(II) center (FIG. 8), as would be generated bystructurally erasing the DMF molecule from 3. The Cu[Au(CN)₂]₂ systemwas found to be only slightly porous by N₂-adsorption measurements,suggesting that the 2-D sheets stack in an offset fashion, likely withsignificant aurophilic interactions, thereby blocking channel formation.Despite this, solvents are still taken up by this system to yield thesame Cu[Au(CN)₂]₂(solvent), complexes.

Concentration-controlled synthesis of structural isomers of coordinationpolymers Results obtained by X-ray crystallography and elementalanalysis indicate that 1 and 2 of this Example are true polymorphs orsupraniolecular isomers, as opposed to pseudopolymorphs that differ byincorporation of varying amounts or identities of co-crystallizedsolvent molecules.^(3,4) As mentioned above, many factors contribute tothe preferential formation of one polymorph over another and it canoften be a challenge to control the synthesis of a desired isomer.³⁻⁷Varying crystallization conditions, such as solvent type, startingmaterials, temperature and concentration are often important to ensuregeneration of just one polymorph. For example, crystallizingNi[Au(CN)₂]₂(en)₂ (en=1,2-ethylenediamine) from [Ni(en)₃]Cl₂.2H₂O or[Ni(en)₂Cl₂] generates molecular and 1-dimensional polymorphic materialsrespectively.³⁴ Also, it has been shown that metastable polymorphs canbe obtained by rapid crystallization from a supersaturated solution,e.g., via a fast drop in temperature.^(6,42) For example,{Cu[N(CN)₂]₂(pyrazine)}_(n) forms green/blue and blue polymorphs whencrystallized from concentrated and dilute solution respectively.⁴³

Similarly, in the Cu[Au(CN)₂]₂(DMSO)₂ system described in this Example,if the total concentration of reagents is below 0.2 M, 1 is formed,while 2 is obtained exclusively from >0.5 M solutions. Theconcentration-controlled synthesis of structural isomers of coordinationpolymers is uncommon relative to examples with molecularsystems.^(43,44) This concentration dependence suggests that green 1 isthe thermodynamic product, while blue 2, which rapidly precipitates fromsolution, is likely a kinetic product. The fact that Cu[Au(CN)₂]₂(H₂O)₂converts exclusively to the green polymorph 1 when adsorbing DMSO isfurther evidence that 1 is the most energetically favorable polymorph.Interestingly, the density of thermodynamically preferred 1 is actuallylower than that of 2. This surprising situation has been observed inother polymolphs.⁸ Although it is unclear if this result can beattributed to entropic or enthalpic contributions, it is conceivablethat the formation of shorter Au—Au bonds in 1 relative to 2 could be animportant energetic factor.

Metal-ligand superstructures It has been recognized that a system doesnot need to be porous in order to undergo guest uptake.⁴⁵ For example, aflexible metal-ligand superstructure can dynamically adapt in order toaccommodate a variety of potential guests.⁴⁵⁻⁵¹ In this light, theJahn-Teller influenced flexible coordination sphere and the greaterlability of Cu^(II) compared with other transition metals are likelyimportant features of the Cu[Au(CN)₂]₂(solvent)_(x) system. The relatedMn[Au(CN)₂]₂(H₂O)₂ and Co[Au(CN)₂]₂(DMF)₂ systems previously reportedform more rigid frameworks.^(40,41) For these two systems, thermaltreatment is required to remove the guest molecules and yield compoundsexhibiting zeolitic properties. The lability of Cu^(II) in the system ofthe present invention facilitates the reversible exchange of adsorbedsolvent molecules without any thermal treatment required. It also likelyincreases the flexibility of the framework by allowing the breaking andthe reformation of Cu—N(cyano) bonds, thereby adapting to the solventguest present. Gold-gold interactions are probably present in all theCu[Au(CN)₂]₂(solvent)_(x) complexes and help to stabilize the 3D-networkas solvent exchange takes place.

Taking into account the varied structures of theCu[Au(CN)₂]₂(solvent)_(x) complexes, several modes of flexibility withinthe fundamental structural framework, i.e. the two-dimensionalsquare-grid network of the Cu[Au(CN)₂]₂ moiety (FIG. 8), can beidentified. Firstly, the 2-D square-grid can lie entirely flat, as inthe bis-pyridine or mono-DMF complexes 3 and 4, or it can buckle togenerate a corrugated 2-D array, as observed in the blue bis-DMSOpolymorph 2. The extent of this corrugation can even force the partialfragmentation of the square array via the breaking of one Cu—N(cyano)bond, as observed in the green bis-DMSO polymorph 1. Such fragmentationis probably also present in the Cu[Au(CN)₂]₂(NH₃)₄ complex (9); theCu^(II) center in 9 is likely still octahedral, with two Cu—N(cyano)bonds (out of four in the fundamental square-grid structure) breakingcompletely to make way for two additional NH₃ ligands, therebydisrupting the 2-D array. Another mode of flexibility lies in theability of the Cu^(II) center to readily alternate between being five-and six-coordinate, as well as accessing a range of five-coordinategeometries. This adaptability is independent of the extent ofcorrugation: five-coordinate Cu^(II) centers are found in both flat 3and corrugated 1 while six-coordinate centers are present in both flat 4and corrugated 2. Finally, the Jahn-Teller distortions endemic toCu^(II) complexes yield a third mode of flexibility: the arrangement ofequatorial/axial or basal/apical N(cyano) ligands and donor solvents.Again, this pliability is independent of the extent of corrugation: boththe five-coordinate DMF complex 3 and six-coordinate bis-pyridinecomplex 4 contain flat Cu[Au(CN)₂]₂ square-grids, but in 3 the N(cyano)ligands are all basal (and therefore roughly identical in length) whilein 4 two N(cyano) ligands are equatorial and two are axial, leading tosignificantly different Cu—N(cyano) bond lengths. This form ofstructural flexibility is particularly important since substantiallydifferent IR signatures in the cyanide region are generated depending onthe N(cyano) bonding arrangement in the system. Of course, all threemodes of flexibility work in concert to generate the adaptable, dynamicnetwork solid that is ultimately able to bind and sense different donorsolvents.

The source of the vapochromism in the Cu[Au(CN)₂]₂(solvent), systemdiffers from that of other Au^(I)-containing systems.⁹⁻¹²Cu[Au(CN)₂]₂(solvent)_(x) shows vapochromism in the visible since eachdonor solvent molecule that is adsorbed binds to the Cu^(II) center andmodifies differently the crystal field splitting. As a consequence, thecolour of the vapochromic compound changes as the d-d absorption bandsshift with donor. In addition to donor identity, the resultingcoordination number (five or six) and specific geometry of the coppercenter also influences the colour of the complexes by altering thesplitting of the d-orbitals.

The [Au(CN)₂]⁻ unit is also a key component of this system since ittelegraphs the changes in solvent bound to the Cu^(II) centers via theν_(CN) stretch. Each Cu[Au(CN)₂]₂(solvent)_(x) has a different IRsignature since every VOC modifies in a different manner the electrondensity distribution around the Cu^(II) center. This influences theamount of π-back bonding from the Cu^(II) center to the CN group, whichin turn is observed in the IR spectrum due to the change in vibrationfrequency.²⁷ Also, the number of bands observed is related to thesymmetry and coordination number of the Cu^(II) centers, as described indetail above.

In summary, it has been illustrated in this Example that, despite theirdifferent solid-state structures, the two Cu[Au(CN)₂]₂(DMSO)₂ polymorphsexhibit the same vapochromic behaviour with respect to sorption ofanalytes such as VOCs. The use of [Au(CN)₂]⁻ as a building block isimportant to the function of this vapochromic coordination polymer.First, it provides the very sensitive CN reporter group that can allowIR-identification of the solvent adsorbed in the materials. Also, Au—Auinteractions via the [Au(CN)₂]⁻ units increase the structuraldimensionality of the system in most cases and probably help providestabilization points for the flexible Cu[Au(CN)₂]₂ framework.

Example 2.0 2.1 Zn[Au(CN)₂]₂(solvent)_(x) System

Synthesis of Zn[Au(CN)₂]₂(DMSO)₂. To a 1 mL DMSO solution ofZn(ClO₄)₂(H₂O)₆ (0.032 g, 0.086 mmol) was added KAu(CN)₂ (0.050 g,0.173). Slow evaporation yielded crystals of Zn[Au(CN)₂]₂(DMSO)₂. Anal.Calcd. for C₈H₁₂N₄Au₂O₂S₂Zn: C, 13.35; H, 1.68; N, 7.79%. Found: C,13.50; H, 1.72; N, 8.04%. IR (KBr, cm⁻¹) 3009 (in), 2919(m), 2849(w),2186(s), 2175(s), 1409(m), 1314(m), 1299(m), 1031(m), 1013(s), 1005(s),957(m), 710(w).

Although the structure of a solvent-free Zn[Au(CN)₂]₂ polymer is known,it is believed that no luminescence or analyte binding properties havepreviously been reported. FIG. 9 consists of photographs showing changesin luminescence in a Zn[Au(CN)₂]₂(analyte)_(x) system under room light(top) and ultraviolet light (bottom). From left to right the analyte isNone, NH₃, pyridine, CO₂ and DMSO. As in Example 1.0 above, thecyanide-IR changes are also dramatic and distinctive for each analyte.

The zinc-based polymer described herein appears to bind CO₂: Anal.Calcd. for C₅N₄Au₂O₂Zn: C, 9.89; H, 0.00; N, 9.22%. Found: C, 9.73; H,0.00; N, 9.32%. IR (KBr, cm⁻¹): 2192 (s).

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many alterations and modifications are possible inthe practice of this invention without departing from the spirit orscope thereof. Accordingly, the scope of the invention is to beconstrued in accordance with the substance defined by the followingclaims. TABLE 1 Crystallographic Data and Structural Refinement Details1 (Green) 2 (Blue) 3 4 empirical C₈H₁₂N₄Au₂CuO₂S₂ C₈H₁₂N₄Au₂CuO₂S₂C₇H₇N₅Au₂CuO C₁₄H₁₀N₆Au₂ formula fw 717.82 717.82 634.65 719.76 Crystalsystem monoclinic triclinic monoclinic monoclinic Space group C2/c P 1C2/c P2₁/c a, Å 11.5449(15) 7.874(7) 12.8412(10) 7.3438(7) b, Å14.191(4) 12.761(11) 14.5056(8) 14.1201(10) c, Å 11.5895(12) 16.207(13)13.9932(9) 8.2696(6) α, deg 90 89.61(7) 90 90 β, deg 112.536(9) 82.29(7)96.064(3) 94.082(3) γ, deg 90 88.57(7) 90 90 V, Å³ 1753.8(6) 1613.2(24)2591.9(3) 855.34(12) Z 4 2 8 4 T, K 293 293 293 293 λ, Å 0.70930 1.541801.54180 1.54180 ρ_(calcd), g ^(·) cm⁻³ 2.719 2.955 3.253 2.794 μ, mm⁻¹18.079 37.500 43.542 33.103 R₁ ^(a) (I > xσ(I))^(b) 0.042 0.062 0.0320.028 wR₂ ^(a) (I > xσ(I))^(b) 0.047 0.082 0.046 0.040 Goodness of fit2.20 1.38 0.93 1.00^(a)Function minimized Σw(|F_(o)| − |F_(c)|)² where w⁻¹ = σ²(F_(o)) +0.0001F_(o) ², R = Σ∥F_(o)| − |F_(c)∥/Σ|F_(o)|, R_(w) = [Σ

|F_(o)| − |F_(c)|)²/Σw|F_(o)|²)^(1/2).^(b)For 1, x = 2.5; for 2, 3 and 4, x = 3.

TABLE 2 Selected bond lengths (Å) and angles (°) for Cu[Au(CN)₂]₂(DMSO)₂(1). Au(1)-Au(2) 3.22007(5) Cu(1)-N(2) 2.107(18) Cu(1)-O(1) 1.949(7)Cu(1)-N(3) 1.965(11) O(1)-Cu(1)-O(1*) 167.0(6) Cu(1)-N(2)-C(2) 180O(1)-Cu(1)-N(2) 96.5(3) Cu(1)-N(3)-C(3) 178.6(12) O(1)-Cu(1)-N(3)87.3(4) Au(2)-Au(1)-Au(2) 171.73(3) O(1*)-Cu(1)-N(3) 88.4(4)Au(1)-N(1)-C(1) 180 N(2)-Cu(1)-N(3) 109.5(4) Au(1)-N(2)-C(2) 180N(3)-Cu(1)-N(3*) 140.9(8) Au(2)-N(3)-C(3) 178.9(12) Cu(1)-O(1)-S(1)127.2(6) C(1)-Au(1)-C(2) 180Symmetry transformations: (*) −x + 1, y, −z + 1/2; (′) −x + 1/2, −y −5/2, z + 1.

TABLE 3 Selected bond lengths (Å) and angles (°) for Cu[Au(CN)₂]₂(DMSO)₂(2) Au(1)-Au(2) 3.419(3) Au(3) . . . Au(4) 3.592(4) Cu(1)-O(1) 2.02(3)Cu(2)-O(3) 1.97(3) Cu(1)-O(2) 1.95(3) Cu(2)-O(4) 2.29(3) Cu(1)-N(11)2.42(4) Cu(2)-N(12) 2.11(4) Cu(1)-N(21) 1.97(4) Cu(2)-N(22) 2.37(5)Cu(1)-N(31) 2.42(4) Cu(2)-N(32) 2.03(5) Cu(1)-N(41) 1.99(4) Cu(2)-N(42)2.00(5) O(1)-Cu(1)-O(2) 95.2(12) O(3)-Cu(2)-O(4) 93.0(12)O(1)-Cu(1)-N(11) 85.9(12) O(3)-Cu(2)-N(12) 87.8(15) O(2)-Cu(1)-N(11)86.4(12) O(4)-Cu(2)-N(12) 87.0(14) N(11)-Cu(2)-N(21) 92.7(14)N(12)-Cu(2)-N(22) 92.3(16) N(11)-Cu(2)-N(31) 172.7(13) N(12)-Cu(2)-N(32)172.0(17) N(11)-Cu(2)-N(41) 92.6(14) N(12)-Cu(2)-N(42) 95.2(17)N(21)-Cu(2)-N(31) 92.6(15) N(22)-Cu(2)-N(32) 91.4(17) N(21)-Cu(2)-N(41)90.7(15) N(22)-Cu(2)-N(42) 91.2(17) N(31)-Cu(2)-N(41) 92.3(14)N(32)-Cu(2)-N(42) 91.8(18) Cu(1)-O(1)-S(1) 124.9(17) Cu(2)-O(3)-S(3)125.4(20) Cu(1)-O(2)-S(2) 124.4(19) Cu(2)-O(4)-S(4) 127.9(18)Cu(1)-N(11)-C(11) 169.2(45) Cu(2)-N(12)-C(12) 163.5(50)Cu(1)-N(21)-C(21) 163.5(41) Cu(2)-N(22)-C(22) 159.5(46)Cu(1)-N(31)-C(31) 161.7(43) Cu(2)-N(32)-C(32′) 174.6(45)Cu(1)-N(41)-C(41) 166.4(33) Cu(2)-N(42)-C(42) 170.0(45)C(11)-Au(1)-C(12) 172.7(25) C(31)-Au(3)-C(32) 172.6(18)C(21)-Au(2)-C(22*) 175.9(23) C(41*^(b))-Au(4)-C(42) 177.9(20)Au(1)-C(11)-N(11) 175.8(50) Au(3)-C(31)-N(31) 171.0(39)Au(1)-C(12)-N(12) 175.3(58) Au(3)-C(32)-N(32′^(b)) 175.6(49)Au(2)-C(21)-N(21) 173.2(42) Au(4*^(b))-C(41)-N(41) 174.2(38)Au(2*)-C(22)-N(22) 175.2(56) Au(4)-C(42)-N(42) 170.1(46)Symmetry transformations: (*) −x + 1, −y + 1, −z + 1; (*^(b)) −x + 1,−y, −z + 1; (′) x + 2, y, z − 1; (′^(b)) x − 2, y, z + 1.

TABLE 4 Selected bond lengths (Å) and angles (°) for Cu[Au(CN)₂]₂(DMF)(3). Au(1)-Au(1*^(a)) 3.3050(12) Cu(1)-N(2) 1.990(11) Au(2)-Au(2*^(b))3.1335(13) Cu(1)-N(3) 1.961(10) Cu(1)-O(1) 2.202(12) Cu(1)-N(4′^(b))1.982(10) Cu(1)-N(1′) 1.958(10) O(1)-C(5) 1.202(17) N(1′^(a))-Cu(1)-N(2)89.8(4) C(1)-Au(1)-C(2) 176.0(6) N(1′^(a))-Cu(1)-N(3) 88.7(5)C(3)-Au(2)-C(4) 175.4(6) N(4′^(b))-Cu(1)-N(2) 89.6(5)Cu(1′^(c))-N(1)-C(1) 170.1(12) N(4′^(b))-Cu(1)-N(3) 89.3(5)Cu(1)-N(2)-C(2) 172.7(14) N(1′^(a))-Cu(1)-N(4′^(b)) 166.7(5)Cu(1)-N(3)-C(3) 170.8(12) N(2)-Cu(1)-N(3) 169.2(5) Cu(1′^(d))-N(4)-C(4)172.1(12) O(1)-Cu(1)-N(1′^(a)) 95.1(5) Au(1)-C(1)-N(1) 174.9(13)O(1)-Cu(1)-N(2) 98.3(5) Au(1)-C(2)-N(2) 177.8(14) O(1)-Cu(1)-N(3)92.4(5) Au(2)-C(3)-N(3) 174.3(13) O(1)-Cu(1)-N(4′^(b)) 98.1(5)Au(2)-C(4)-N(4) 177.5(16) Cu(1)-O(1)-C(5) 125.4(13)Symmetry transformations: (*^(a)) −x − 1, y, −z + 3/2; (*^(b)) −x − 1,y, −z + 1/2; (′^(a)) x, −y, z − 1/2; (′^(b)) x, −y − 1, z + 1/2; (′^(c))x, −y, z + 1/2; (′^(d)) x, −y − 1, z − 1/2.

TABLE 5 Selected bond lengths (Å) and angles (°) forCu[Au(CN)₂]₂(pyridine)₂ (4). Cu(1)-N(1) 2.016(9) Cu(1)-N(3) 2.007(7)Cu(1)-N(2*^(a)) 2.532(9) N(1)-Cu(1)-N(2*^(a)) 89.5(4) C(2)-Au(1)-C(1)177.8(4) N(1′)-Cu(1)-N(2*^(a)) 90.5(4) Cu(1)-N(1)-C(1) 169.7(9)N(1)-Cu(1)-N(3) 90.0(3) Cu(1*^(b))-N(2)-C(2) 173.3(9) N(1)-Cu(1)-N(3′)90.0(3) Au(1)-C(1)-N(1) 177.9(9) N(2*^(a))-Cu(1)-N(3) 90.4(3)Au(1)-C(2)-N(2) 177.2(11) N(2*^(a))-Cu(1)-N(3′) 89.6(3)Symmetry transformations: (*^(a)) x − 1, −y + 1/2, z − 1/2; (*^(b)) x +1, −y + 1/2, z + 1/2; (′) −x + 1, −y, −z + 1.

TABLE 6 Maximum Solid-state Visible Reflectance (nm) and Cyanide ν_(CN)Absorptions (cm⁻¹) for Different Cu[Au(CN)₂]₂(solvent)_(x) ComplexesMaximum visible ν_(CN) absorption(s) Complex reflectance From solutionFrom adsorption^(a) (1) Cu[Au(CN)₂]₂(DMSO)₂ 550 ± 7 2183(s), 2151(s)2184(s), 2151(s) (from 5) (2) Cu[Au(CN)₂]₂(DMSO)₂ 535 ± 15 2206(m),2193(s), 2175(m), — (broad) 2162(m) (3) Cu[Au(CN)₂]₂(DMF) 498 ± 72199(s) 2199 (s) (4) Cu[Au(CN)₂]₂(pyridine)₂ 480 ± 15 2179(m), 2167(s),2152(m), 2179(m), 2167(s), (broad) 2144(m) 2152(m), 2144(m) (5)Cu[Au(CN)₂]₂(H₂O)₂ 535 ± 5 2217(s), 2194(w), 2172(s) 2217(s), 2194(w),2171(s) (from 1) 2216(s), 2196(w), 2171(s) (from 2) (6) Cu[Au(CN)₂]₂ 560± 20 2191(s) — (v. broad) (7) Cu[Au(CN)₂]₂(CH₃CN)₂ — 2297(w), 2269(w),2191(s) (8) Cu[Au(CN)₂]₂(dioxane)(H₂O) 505 ± 15 2201(s), 2172(w)2200(s), 2174 (w) (broad) (9) Cu[Au(CN)₂]₂(NH₃)₄ 433 ± 7 — 2175(m),2148(s)^(a)All solvent adducts were made from 2 unless specified

TABLE 7 Thermal Decomposition of Different Cu[Au(CN)₂]₂(solvent)_(x)Complexes Temperature Decomposition product Weight (%) Complex (° C.) orlost fragment calcd found 3 195-280 -DMF 11.5 13.6 310-355 -2 C₂N₂ + O13.8 11.5 400 CuO + 2 Au 74.6 73.9 4 155-190 - 1 pyridine 11.0 10.9210-260 - 1 pyridine 11.0 12.6 310-330 - 2 C₂N₂ + O 12.2 9.2 400 CuO + 2Au 65.8 66.4 5 140-180 - 2 water 6.0 5.5 260-380 -2 C₂N₂ + O 14.7 13.5400 CuO + 2 Au 79.2 81.5 6 200-350 -2 C₂N₂ + O 15.2 15.5 400 CuO + 2 Au81.7 80.9 8 150-280 - dioxane - H₂O 15.9 17.5 290-330 -2 C₂N₂ + O 13.210.3 400 CuO + 2 Au 70.9 71.1 9 50-95 - 1 NH₃ 2.7 2.8 115-220 - 3 NH₃8.1 7.5 280-350 -2 C₂N₂ + O 14.0 13.7 400 CuO + 2 Au 75.2 74.4

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1. A vapochromic polymer comprising:M_(W)[M′_(X)(Z)_(Y)]_(N) wherein M and M′ are the same or differentmetals capable of forming a coordinate complex with the Z moiety; Z isselected from the group consisting of halides, pseudohalides, thiolates,alkoxides and amides; W is between 1-6; X and Y between 1-9; and N isbetween 1-5.
 2. The polymer as defined in claim 1, wherein W and X are1, Y is 2, and N is
 2. or
 3. 3. The polymer as defined in claim 2,wherein said polymer is reversibly vapochromic.
 4. The polymer asdefined in claim 1, wherein M is a transition metal.
 5. The polymer asdefined in claim 1, wherein M′ is a metal selected from the groupconsisting of Au, Ag, Hg and Cu.
 6. The polymer as defined in claim 1,wherein Z is a pseudohalide selected from the group consisting of CN,SCN, SeCN, TeCN, OCN, CNO and NNN.
 7. The polymer as defined in claim 1,wherein M is selected from the group consisting of Cu, Zn, Sc, Ti, V,Cr, Mn, Fe, Co and a lanthanide.
 8. The polymer as defined in claim 7,wherein M is Cu or Zn.
 9. The polymer as defined in claim 1, wherein M′is selected from the group consisting of Au and Ag and wherein Z is CN.10. The polymer as defined in claim 9, wherein M′ is Au and wherein X is1 and Y is
 2. 11. The polymer as defined in claim 1, further comprisingan organic ligand bound to M.
 12. The polymer as defined in claim 11,wherein said organic ligand comprises at least one nitrogen, oxygen,sulphur or phosphorus donor.
 13. The polymer as defined in claim 1,further comprising a counterbalancing cation or anion.
 14. The polymeras defined in claim 1, wherein said polymer is vapoluminescent.
 15. Thepolymer as defined in claim 1, wherein X=1 and Y=2.
 16. A compositioncomprising a polymer as defined in claim 1, and an analyte adsorbed tosaid polymer.
 17. The composition as defined in claim 16, wherein saidanalyte is a volatile organic compound.
 18. The composition as definedin claim 16, wherein said analyte is a gas having a donor hydrogen,nitrogen, oxygen, sulphur or phosphorus atom.
 19. A solid-statevapochromic structure comprising a polymer as defined in claim
 1. 20. Asolid-state vapochromic structure comprising a composition as defined inclaim
 16. 21. The use of a structure a defined in claim 19 forvapochromically sensing the presence of an analyte.
 22. An analyte-boundcomplex comprising an analyte adsorbed to a polymer as defined inclaim
 1. 23. A method of detecting an analyte comprising: (a) providinga polymer as defined in claim 1; (b) exposing said polymer to a supplyof said analyte; and (c) detecting any chromatic changes in said polymerresulting from exposure to said analyte.
 24. The method as defined inclaim 23, wherein said detecting comprises sensing any changes in thecolour of said polymer.
 25. The method as defined in claim 23, whereinsaid detecting comprises sensing any changes in the luminescence of saidpolymer.
 26. The method as defined in claim 23, wherein said detectingcomprises spectroscopically identifying any changes in the infraredsignature of said polymer.
 27. The method as defined in claim 26,wherein said spectroscopically identifying comprises detecting thenumber and position of ν_(CN) spectroscopic bands.
 28. The method asdefined in claim 23, wherein said chromatic changes are reversible. 29.The method as defined in claim 28, wherein said supply comprisesdifferent analytes and wherein steps (b) and (c) are dynamicallyrepeated in respect of successive ones of said analytes.
 30. The methodas defined in claim 23, wherein M is Cu or Zn and wherein M′ is Au. 31.The method as defined in claim 30, wherein said polymer is selected fromthe group consisting of Cu[Au(CN)₂]₂ and Zn[Au(CN)₂]₂.
 32. The method asdefined in claim 23, wherein said analyte is a volatile organiccompound.
 33. The method as defined in claim 23, wherein said analyte isa gas.
 34. The method as defined in claim 29, wherein said gas is CO andCO₂.
 35. The use of a polymer as defined in claim 1 for vapochromicallysensing the presence of an analyte.
 36. A method of synthesizing apolymer as defined in claim 8 comprising reacting a Cu(II) or a Zn(II)salt with [Au(CN)₂]⁻ in a solvent.
 37. A vapochromic compositioncomprising a metal complex represented by the general formulaM_(W)[M′_(X)(Z)_(Y)]_(N) wherein M and M′ are the same or differentmetals capable of forming a coordinate complex with the Z moiety; Z isselected from the group consisting of halides, pseudohalides, thiolates,alkoxides and amides; W is between 1-6; X and Y between 1-9; and N isbetween 1-5.
 38. The composition as defined in claim 37 wherein; M isselected from the group consisting of Cu and Zn; M′ is selected from thegroup consisting of Au, Ag, Hg and Cu; Z is a pseudohalide selected fromthe selected from the group consisting of CN, SCN, SeCN, TeCN, OCN, CNOand NNN; W and X are 1; Y is 1; and N is 2 or 3.